Unhexpentium
Unhexpentium, Uhp, is the temporary name for element 165. It is expected to be a transient element, one without long-lived isotopes or long-lived precoursers. Uhp may form during neutron star mergers. Properties NUCLEAR At least one model exists predicting the half-lives and decay modes for nuclides up to Z = 175 and N = 333(1), which includes isotopes Uht 496 and lighter. It is helpful to view p 18 of Ref. 1, which maps predicted half-lives of nuclides in this region, and p 15, which maps principal decay modes. These maps are the result of large extrapolations from what can be tested, though. Half-lives are accurate only to within three orders of magnitude and decay modes give no information about competing minor decay modes. Results given in this article should be regarded as tentative. Ref. 1 predicts a band of nuclides ranging from Uhp 450 to Uhp 473. As neutron count increases in this band, half-life increases, reaching a maximum around a second, while principal decay mode shifts from fission to alpha emission . Above this is a band of alpha-emitting isotopes with sub-millisecond half-lives between Uhp 474 and Uhp 484. Above Uhp 484, only the fission-decaying isotopes Uhp 493 and Uhp 494 are reported to survive for more than 10^-09 sec. The entire range from Uhp 450 to Uhp 498 is what one expects for a shell closure at N = 308. There is no indication of stabilization by any other shell closures. Beyond Uhp 498, predicting nuclear properties is largely guesswork. At least two sets of predictions exist for location of the neutron dripline up to Z = 175(3),(4). These two indicate that the dripline occurs between Uhp 566 and Uhp 596. Neutron shell closures are also predicted to occur at N = 370(3) and 406(5). Ref. 5 also includes predicted structural correction energies provided by shell closures at N = 406 and Z = 164. Multiplying the Z = 164 corrective energy of Ref. 5 by 0.7, as was required for consistency at Z = 164 (see Unhexquadium, this wiki) leads to a prediction that isotopes between Uhp 510 and Uhp 596 will decay principally by beta emission, with a significant beta-decay branch occurring as low as Uhp 501. The band from Uhp 510 to Uhp 566 is particularly important, since it lies below the lower neutron dripline prediction, strongly implying that these isotopes will beta decay. The N = 370 closure doesn't expand this range, but will enhance stability in a band which may be as wide as Uhp 525 to Uhp 540. ATOMIC There is some uncertainty about the electron structure of Uhp with some sources classifying it as a transition metal (d-block) and others as a p-block element. This is of importance only to atomic theory, since the element is never found in an environment cool enough to have chemistry. Of more importance, its last (1s) ionization energy appears to be in the range 745 - 865 keV, meaning that bare nuclei are abundant only at temperatures above 7 gK. Electron configuration predicted for Uhp takes account of finite nuclear size, but nuclear shape is neither considered nor dismissed explicitly. Nuclear shape may have some effect on electron structure. Formation Polar jets emanating from young neutron stars and black holes function like giant, sloppy particle accelerators. It is possible for fusion or multinucleon transfer reactions to produce all isotopes of Uhp, but only in atoms-per star quantities. This section addresses possible isotopes which can form in quantity. Material originally found 800-1000 m beneath the surface is expected to be ejected from a neutron star when it disintegrates during a merger. This material will consist of nuclides at or near the neutron dripline and having a proton count which may go as high as Z = 170. A zone of beta-decaying nuclides extending from the dripline to Uhp extends as low as A = 547, implying that the isotopes between Uhp 532 and Uhp 566 are likely to form in quantity (taking b+x*n decay into account), and that isotopes between Uhp 567 and Uhp 596 are possible, depending on where the dripline actually occurs. These nuclei will have millisecond-scale half-lives. Neutron capture is unlikely to produce more than an atom or two per star of nuclides heavier than A = 350. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. 3. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 4. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 5. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. (02-14-20) References Category:Undiscovered elements Category:Pnictogens Category:Radioactive